"On the average, each person should get about 64 ounces of water. Anything caffeine-free, calorie-free is what I'm looking for," said registered dietician Natalie Newell.

Newell said purified water is the best choice. In the grocery aisles, some water products also offer flavor and vitamins, but Newell said to play close attention to the serving per container because it may contain more calories than you expect.

Extra calories can also be a problem with most sports drinks. They replace nutrients lost during intense exercise.

"Most of us aren't doing enough activity that we need to replenish electrolytes," Newell said.

Plain water is enough for Kim Brown and Barbara Weaver when they hit the gym.

"I think it just makes you feel better," Weaver said.

"I know that it helps you to lose weight and that's a big thing too, but most of it is because I know it's supposed to be good for you," Newell said.

What you drink only represents 80 percent of your water intake. The other 20 percent comes through food. Many fruits and vegetables, like cucumbers and watermelon, are nearly 100 percent water.